(1) Field of the Invention
The present invention relates generally to sonar processing and, more particularly, to a post processing method for estimating range and depth for one or more acoustically radiating sources by correlation processing between the passively received signal and an environmentally modeled signal.
(2) Description of the Prior Art
Many traditional sonar systems provide only an estimation of the bearing from a platform to one or more radiating underwater acoustic sources of interest. It would be advantageous to obtain range and depth information to the one or more acoustic sources of interest. If for no other reason, the performance of a sonar system can be enhanced by rapid estimation of range and depth to a radiating underwater acoustic source. Prior art techniques for obtaining range and depth are discussed below and may typically require knowledge about the depth of the source or involve the use of vertical sensor arrays with beamforming techniques, or variable depth sonars, or the like.
The following U.S. patents describe various prior art systems that may be related to the above and/or other telemetry systems:
U.S. Pat. No. 4,312,053, issued Jan. 19, 1982, to Lipsky, discloses a method and apparatus for computing the range to and depth of a submerged object that either emits or reflects pulses of acoustic energy, wherein a detecting array and related data handling apparatus measure as a function of time the apparent angles of arrival of the acoustic energy associated with each such pulse. This data is then translated into actual multipath arrival angles and multipath travel time differences which are utilized to solve mathematical equations, the solutions of which result in the calculation of the range to and depth of the submerged source of acoustic energy.
U.S. Pat. No. 5,420,827, issued May 30, 1995, to Feintuch, discloses a variable depth sonar which is adapted to provide passive multipath target ranging and depth estimates. The sonar employs a novel estimation procedure which is adapted to sonars with relatively small sensors and limited computing power. A novel feature of the invention is the introduction of a change of depth of the sonar receiver, mounted on a mobile platform, into the estimation process. Measurements at the two different depths are combined to provide target range and depth. Other features and improvements are disclosed.
U.S. Pat. No. 5,455,806, issued Oct. 3, 1995, to Hutson, discloses a multi-dimensional acoustic data processing and display system that arranges acoustic data in a three-dimensional matrix. The three-dimensional matrix is compressed using singular value decomposition into singular vectors and singular values. A historical database is created and maintained and is also concatenated with the three-dimensional data. This database allows reverberation and noise to be diminished and other, weaker features in the data to be enhanced. Once the data is compressed, the data can be analyzed efficiently. The singular vectors are partitioned into one or more groups on the basis of their singular values or other criteria. Certain of the compressed data elements are enhanced or diminished by modifying the singular values within each of the groups of singular vectors. Selected singular vectors are processed further by other techniques for further enhancement, detection, isolation, feature extraction and classification. The compressed and enhanced data is then expanded back into three-dimensional form for display or for other processing.
U.S. Pat. No. 5,481,505, issued Jan. 2, 1996, to Donald et al, discloses a method and apparatus for detecting, processing and tracking sonar signals to provide bearing, range and depth information that locates an object in three-dimensional underwater space. An “inverse beamformer” utilizes signals from a towed horizontal array of hydrophones to estimate a bearing to a possible object. A “matched field processor” receives measured covariance matrix data based upon signals from the hydrophones and signals from a propagation model. An eight nearest neighbor peak picker provides plane wave peaks in response to output beam levels from the matched processor. A five-dimensional M of N tracker identifies peaks within the specified limit of frequency, bearing change over time, range and depth to specify an object as a target and to display its relative range and depth with respect to the array of hydrophones.
U.S. Pat. No. 5,914,912, issued Jun. 22, 1999, to Yang, discloses a sonar array post processor that employs an adaptive processing, known as matched beam processing, in the beam domain which takes analog or digital conventional beamforming outputs from a sonar array, multiplies them by a set of adaptive weighting coefficients and produces a new set of beams. The new output beam of highest intensity yields the ideal maximum signal gain and correct target bearing. Continuous target tracking provided by the sonar array post processor in the endfire direction of a horizontal line array minimizes the towing ships maneuvers and for, a bottom mounted surveillance system, a smaller number of arrays are required.
U.S. Pat. No. 6,009,045, issued Dec. 28, 1999, to Yang et al, discloses an advanced vertical array beamformer signal processor that accomplishes acoustic beamforming of an underwater vertical array used in shallow water utilizing matched beam processing to suppress generated noise and/or ship radiated noise thereby increasing the detectability of a submerged source emitting only a low noise signal. The processor exploits the difference of the signal arrival angle of both active and passive signals with that of the wind generated noise and ship radiated noise which is prominent in downward refractive sound speed profiles. After filtering the undesired noise, the processor uses the depth of the source as a clue for detection; the processor is an energy detector focused on the returns of a deep source.
U.S. Pat. No. 6,096,085, issued Aug. 1, 2000, to Sammelman, discloses a computer-readable software stored on a storage medium and executed on a computer to perform an integrated sonar simulation, including a parameter definition code for defining a plurality of parameters of a sonar, target and sonar environment, and a SNR computation code for computing a SNR of the sonar as a function of range to target, based upon the parameters defined by the parameter definition code. The parameters defined by the parameter definition code include ambient noise, volume scattering strength of the sonar environment, sound velocity profile of the sonar, beam patterns of both projector and receiver of the sonar, type of sonar, range resolution of the sonar, number of eigenrays striking the surface and bottom of the sonar environment, number of eigenrays striking the target, ray trajectories to the target, and surface and bottom scattering strength as a function of angle. The software also includes a target strength model generating code for computing scattering from a selected complex target of a stored set of complex target selections, to thereby generate a target strength model for the selected complex target.
U.S. Pat. No. 6,466,891, issued to Carter et al. on Oct. 15, 2002 provides a system that provides a sonar operator with the most likely range to a target of interest. The system generates and displays a contour based on ship's parameters, target parameters, environmental data, and operator parameters. The sonar operator can vary many of the parameters in “what if” scenarios so as to generate groups of contours for preselected probabilities of detection. Contours can be used to show the actions that should be taken to ensure a favorable outcome.
The above cited prior art does not disclose a system which is not limited to vertical arrays, or tracking and beamforming, or which is not an active sonar system, which is operable for determining range and depth. Consequently, those skilled in the art will appreciate the present invention that addresses the above and other problems.